1. Field of the Invention
This invention relates to an interlock assembly for a pair of circuit breakers and, more specifically, to a removal deterrence structure for an interlock assembly wherein the interlock assembly cannot be removed while the enclosure in which the assembly is disposed remains assembled.
2. Background Information
There are a number of applications where it is required that the operation of two circuit breakers be coordinated such that only one circuit breaker can be in the closed, operating position at one time. For example, providing a power-consuming load with electrical power from either of two different sources, such as a commercial power system and an auxiliary supply. It is imperative in such applications that only one circuit breaker be in the closed, operating position at one time. A device that prevents both circuit breakers from being in the operating position is called an interlock.
Circuit breaker interlocks are known which couple the actuating means, for example, operating handles, of circuit breakers whose operation is to be coordinated. One common type of interlock assembly, see e.g. U.S. Pat. No. 5,977,492, includes a sliding panel attached to a shroud. The shroud is disposed over top of the circuit breaker handles. The sliding panel is slidably attached to the shroud and includes cut outs and/or an edge that moves between a position wherein a first circuit breaker handle is blocked and a second circuit breaker handle is free to move and a position wherein the first circuit breaker handle is free to move and the second circuit breaker handle is blocked. As second common type of interlock assembly, see e.g. U.S. Pat. No. 6,043,439, utilizes a sliding bar that moves between a position wherein a first circuit breaker handle is blocked and a second circuit breaker handle is free to move and a position wherein the first circuit breaker handle is free to move and the second circuit breaker handle is blocked. Both the panel type and bar type interlock assemblies, however, have a common disadvantage; both are attached to the exposed portion of the circuit breaker or an exposed portion of the enclosure in which the circuit breaker is disposed. That is, both types of interlock assemblies are typically attached to the top side of the circuit breaker.
Interlock assemblies need to be removed when a circuit breaker is replaced or repaired. As such, the interlock assembly is coupled to the circuit breaker or enclosure by removable fasteners. This is a disadvantage, however, when the interlock assembly may be easily removed. That is, technicians or others may accidentally or intentionally remove the interlock assembly at an improper time, such as when both circuit breakers are still coupled to live circuits. Once the interlock assembly has been removed, there is a great danger that both circuit breakers may be closed at one time.
There is, therefore, a need for a removal deterrence structure for an interlock assembly so that interlock assembly cannot be easily removed from the circuit breakers which the interlock protects.
There is a further need for a removal deterrence structure for an interlock assembly which can only be removed normally during maintenance operations.
There is a further need for a removal deterrence structure for an interlock assembly that cannot be removed while the enclosure in which the circuit breakers are disposed is assembled.
These needs, and others, are addressed by the present invention which provides a removal deterrence structure for an interlock assembly so that the interlock assembly cannot be easily removed while the enclosure in which the circuit breakers are disposed remain assembled. One means of preventing the removal of the interlock assembly is to have the fasteners, which are preferably screws, that couple the interlock assembly to the circuit breakers or the enclosure located on the sides of the circuit breaker or extending in a direction perpendicular to the sides of the circuit breakers. Further, the enclosure in which the circuit breakers are disposed is sized so that the sidewall of the enclosure is adjacent to the fasteners. When the fasteners are disposed in such a manner, the fasteners cannot be accessed from an axial direction. Thus, the fasteners cannot be easily removed as the enclosure in which the circuit breakers are disposed will typically block access to the fasteners. Thus, in order to remove the interlock assembly, the enclosure must be disassembled first. Because disassembly of the enclosure is a time consuming task which is not performed regularly, there is less of a chance that a technician or another will accidentally or intentionally remove the interlock assembly.
The interlock assembly may be either a sliding plate type interlock assembly or a bar type interlock assembly so long as the fasteners that couple the interlock assembly to the enclosure or the circuit breakers extend in a direction parallel to the face, or top side, of the circuit breakers. Alternatively, the invention may be practiced with fasteners that extend in a direction perpendicular to the top side of the circuit breaker so long as the enclosure is structured to prevent access to the fasteners. For example, the enclosure may have guard tabs that extend over the fasteners or a protective lip that extends over the fasteners.